Yes. When you book a Disney package through Costco, like any
travel agency they are simply a pass through, you are actually booking directly with Disney. When you call the Costco Travel reservation number and choose the appropriate prompts you are patched through to Disney Travel Company, though they may answer the phone mentioning something about Costco Travel as well. Costco drives a lot of business to Disney so they are able to offer the perks and discounts that you see on the Costco Travel website. So when you call to book or make payment, you are speaking to Disney directly. I knew from this board that I could book through Costco and pay using Disney gift cards. Another tip, I paid for my little deposit on the trip with my Disney Visa and got the 6 months no interest on that, as I was booking directly with the Disney Travel Company; Costco Travel just being the pass through company.
I am sorry to have caused any confusion on the cash card thing. I mentioned ‘as a general Costco tip’, for purchasing items in the warehouse. Many people already knew that tip, but perhaps many did not! Purchasing a Costco cash card has nothing to do with booking or paying for a vacation package through them. Costco Travel takes regular old credit cards, so yes, you could just make payments on your regular rewards cards. Sorry to not be clear on that!